The present invention relates to a floating type magnetic head and a method for producing floating type magnetic heads for use in a small magnetic disk apparatus. More particularly, it relates to a production method for efficiently performing a cutout machining to restrict the track width of a magnetic head core.
As shown in FIG. 2, a floating type magnetic head (hereinafter sometimes referred to as a "magnetic head") comprises a slider 14b having an air bearing 17, a magnetic head core 1c (hereinafter sometimes referred to as a "head core") fixed by glass 13 to the groove 15 at the flow-out end of the air bearing 17, and a coil (not shown) wound around the magnetic head core.
Methods for producing such a magnetic head include a method in which, as regards a magnetic head core 1c, a pair of magnetic cores, for example, made of Mn-Zn ferrite or the like, or a pair of magnetic cores with a non-magnetic film serving as a magnetic gap and a magnetic metallic thin film formed on a butting surface of at least one of the magnetic cores by sputtering or the like, are bonded and reinforced by bonding glass. After a cutout machining to restrict the track width is performed on the side of the front gap, the magnetic core is inserted into the air bearing groove of a slider, and fixed by a molding glass. Thereafter, the air bearing of the slider or the like are finish-machined, and coils are wound around the magnetic head core a predetermined number of turns, and the core is used in a magnetic disk apparatus.
As handy miniaturized lap-top type and notebook type personal computers have come to be used widely, magnetic disk apparatuses in which the number of disks has increased or 2.5-inch magnetic disk apparatuses in which a 3.5-inch magnetic disk apparatus is more miniaturized have been in demand, while the entire size of the conventional apparatus has been kept as it was before.
In response to such demand as described above, floating type magnetic heads must be made smaller. Magnetic heads have been in demand in which a reference height between a rear or back surface of the magnetic core and an apex thereof is made lower particularly in order to lower the height of the magnetic head. For example, as shown in FIGS. 3A and 3B, the reference height 11c (0.864 mm) is made lower to the reference height 11d (0.61 mm).
Although magnetic heads have been miniaturized, from the viewpoint of their function, the window section of the head core needs a minimum required amount of space in which excitation coils can be wound a predetermined number of turns. In addition, the cross section of the head core needs a predetermined area to secure a magnetic circuit. The more the magnetic head is miniaturized, the more important it is that the limited amount of space be used effectively.
If, for example, a head core having a reference height dimension of 0.61 mm is produced by the same process and procedure as that for a conventional head core having a reference height dimension of 0.864 mm, there is a problem in that the quality and yield of the head cores and the efficiency of the process, or the like are lower in, particularly, a cutout machining process for restricting the track width of a head core than those for a head core having the reference height dimension of 0.864 mm.
A standard procedure for producing conventional magnetic heads is as follows: I core blocks or C core blocks which are made of Mn-Zn ferrite or the like produced by a well-known method, or I core blocks and C core blocks with magnetic metallic thin films formed on the butting surface of at least one of the core blocks, are reinforced and bonded by bonding glass; after a predetermined machining is performed, they are sliced to a certain thickness for each head core; and finish-machining, including lapping, is performed. Next, as shown in FIG. 4, a head core is fixed to a vise-type clamp jig via a buffer material, such as rubber, and the track width is restricted by performing cutting machining using a grinding stone.
When restricting the track width, to secure excellent electromagnetic conversion characteristics, a restriction machining for a cutout surface 22 to restrict the track width of a head core should, at least, be performed at a position of an apex 7, and preferably a position 23 which is deeper than the apex 7. Although the reference height dimension is made small to be 0.61 to 0.66 mm, a space of approximately 0.05 mm must be secured from the front gap surface to the apex of the head core before it is incorporated into the slider. Therefore, if a cutout machining to restrict the track width is performed in a state in which the entire head core is machined to have a height of approximately 0.61 mm which is close to a finished dimension, a chuck allowance of no more than 0.3 to 0.4 mm can be secured. Also, since the cross section of the head core is small, it is not tough enough to be fastened by a vise or the like, and hence the head core is deformed, causing warp. The track width does not fall within the tolerance of a prescribed dimension or the like. Also, there is a problem as regards the quality and yield of the head cores and the efficiency of the process, or the like.
As shown in FIG. 6, when the head core 1d in which a cutout machining to restrict the track width has been completed is inserted into the groove 15 of an air bearing flow-out end of the slider 14b and is fixed by a molding glass 13, the alignment of the heights of the slider and the head core requires an accuracy of .+-.0.005 mm, with the apex serving as a reference. Working conditions are stringent because a clearance between the head core and a side wall which defines a groove can be no more than 0.05 to 0.15 mm. Chipping is caused in the corner of the rear or back surface of the head core at the time of insertion and fixation of the head core, and the cross section of the head core becomes smaller. Thus, there arises a problem in that electromagnetic conversion characteristics of the head core deteriorate or the efficiency of the process becomes lower.
When the air bearing surface is finish-machined after the head core is inserted into the groove of the air bearing of the slider and fixed by a molding glass, a method is also sometimes used in which only a part of side surfaces of the core head near the back gap surface and the side walls which define the groove of the air bearing are bonded by a bonding agent or adhesive to such an extent that they are able to withstand the machining.
Further, in a magnetic head in which only the portion close to the front gap surface is fixed by a molding glass when the head core thereof is inserted into the groove of the air bearing of the slider and fixed by a molding glass and the back gap surface side is in a free state, the amplitude of the vibration transmitted from the slider is amplified and the head core vibrates at a frequency different from that of the slider in an overhung state. The head core expands or contracts in the direction of the height, width and the like thereof, and is deformed, causing a counter magnetostriction phenomenon different from its original magnetized state. The distribution of the magnetization of a magnetic substance forming a magnetic circuit changes, causing the magnetic fluxes of the head core to change. A phenomenon such that the electromagnetic conversion characteristics deteriorate arises often. To prevent such a phenomenon, another method is sometimes employed in which the side surfaces of the head core 1d near the back gap surface are elastically held in the groove of the air bearing by a bonding agent or adhesive, such as a resin 24 or the like, in order that counter magnetostriction can be reduced, as shown in FIG. 7. However, when a bonding agent or resin is made to flow into the side close to the back gap surface, it flows out into the groove before the bonding agent or the like solidifies because the length of the flow-in to the bonded section is small. Thus, a problem remains to be solved, i.e., a sufficient reinforcement cannot be achieved.
When there is a need to hold the side surfaces of the head core near the back gap surface in the groove of the air bearing by using a bonding agent or the like, as described above, the bonding agent or the like adheres on the rear surface of the slider, and the bonding agent or the like solidifies in a projected manner and becomes higher than the rear surface of the slider. Hence, there arises a problem in that the above-described phenomenon hinders the finish-machining of the air bearing or causes deterioration in the accuracy of the air bearing surface.